Golf ball

ABSTRACT

An object of the present invention is to provide a golf ball having good spin performance on approach shots and good shot feeling as well as excellent stain resistance by precisely controlling physical properties of a paint film actually formed on a surface of a golf ball body. The present invention provides a golf ball comprising a golf ball body and a paint film formed on a surface of the golf ball body, wherein the paint film is such that a linear approximation curve obtained by a least square method has a slope in a range from 0.0015 to 0.0045 when a storage modulus (GPa) thereof measured by a nanoindentation method is plotted as a vertical axis against a measuring frequency (Hz) as a horizontal axis, and that an elastic modulus thereof measured by a nanoindentation method ranges from 0.040 GPa to 0.600 GPa.

FIELD OF THE INVENTION

The present invention relates to a golf ball, in particular, a golf ballhaving good spin performance on approach shots and good shot feeling aswell as excellent stain resistance.

DESCRIPTION OF THE RELATED ART

A paint film is formed on a surface of a golf ball body. Conventionally,it has been proposed to improve golf ball properties by improving thepaint film.

For example, Japanese Patent Publication No. 2011-217820 A discloses agolf ball comprising a golf ball body and a paint film formed on asurface of the golf ball body, wherein the paint film has a martenshardness of 2.0 mgf/μm² or less, and a ratio (50% modulus/10% modulus)of 50% modulus of the paint film to 10% modulus of the paint film is 1.6or more. The technology of this Japanese Patent Publication tries toprovide a golf ball having a high spin rate on approach shots under awet condition and a rough condition by the paint film. It is noted that,as the paint film sample for measuring the martens hardness, a paintfilm sheet with a thickness of 100 μm formed from a paint containing abase material and a curing agent, is used (refer to claim 1 andparagraphs 0009, 0057 in Japanese Patent Publication No. 2011-217820 A).

Japanese Patent Publications No. 2013-126541 A, No. 2013-126542 A andNo. 2013-126543 A disclose a golf ball comprising a core located in acenter of the golf ball, a cover surrounding an outside of the core andhaving a plurality of dimples on a surface thereof, and a paint layersurrounding an outside of the cover, wherein the paint layer is formedfrom a material having a Young's Modulus of 70 MPa or less and havingrubber elasticity. The technologies of these Japanese PatentPublications try to provide a golf ball exhibiting a great frictionforce with a golf club and thus having improved spin performance by thepaint layer. It is noted that, as the paint layer sample for measuringthe Young's Modulus, a sample prepared by molding the materials havingeach composition into a sheet shape with a thickness of 2 mm by sprayingfollowed by processing the sheet into a dumbbell-like No. 3 test piecein accordance with JIS K6251, is used. In addition, a loss tangent (tanδ) of the paint layer is also measured, and as the paint layer samplefor measuring the loss tangent (tan δ), a test piece with a thickness of1 mm is used (refer to claims 1, 4 and paragraphs 0014, 0036, 0037, 0058in Japanese Patent Publication No. 2013-126541 A; claims 1, 6 andparagraphs 0015, 0037, 0038, 0059 in Japanese Patent Publication No.2013-126542 A; and claims 1, 5 and paragraphs 0015, 0037, 0038, 0059 inJapanese Patent Publication No. 2013-126543 A).

Japanese Patent Publication No. 2014-014383 A discloses a golf ballcomprising a golf ball body and a paint film formed on a surface of thegolf ball body, wherein the paint film has a storage modulus (E′) of1.00×10⁷ dyn/cm² or more and 1.00×10⁸ dyn/cm² or less at a temperaturerange from 120° C. to 150° C. measured with a dynamic viscoelasticitymeasuring device, and a loss tangent (tan δ) of 0.050 or more at thetemperature of 10° C. The technology of this Japanese Patent Publicationtries to provide a golf ball having excellent controllability onapproach shots of less than 40 yards, especially on approach shots fromaround a green (approximately from 10 yards to 20 yards), and excellentshot feeling. It is noted that, as the paint film sample for measuringthe storage modulus (E′) and the loss tangent (tan δ), a test piece witha thickness of from 0.11 mm to 0.14 mm formed from a paint containing abase material and a curing agent, is used (refer to claim 1 andparagraphs 0013, 0092 in Japanese Patent Publication No. 2014-014383 A).

Japanese Patent Publication No. 2016-123632 A discloses a golf ballcomprising a golf ball body and a paint film formed on a surface of thegolf ball body, wherein a base resin constituting the paint film is apolyurethane obtained through a reaction between a polyol compositionand a polyisocyanate composition, a molar ratio (NCO/OH) of anisocyanate group (NCO group) in the polyisocyanate composition to ahydroxyl group (OH group) in the polyol composition is 0.6 or more, andthe paint film has an elastic modulus of 300 MPa or less. The technologyof this Japanese Patent Publication tries to provide a golf ball havingexcellent shot feeling and stain resistance by the paint film. It isnoted that the elastic modulus of the paint film is directly measured onthe paint film formed on the surface of the golf ball with a scanningprobe microscope in an atomic force microscope mode (refer to claim 1and paragraphs 0009, 0060 in Japanese Patent Publication No. 2016-123632A).

SUMMARY OF THE INVENTION

However, the golf balls provided in the technologies of the abovementioned Japanese Patent Publications do not always have satisfactoryvarious performances such as spin performance on approach shots, shotfeeling and stain resistance, there is still room for improvement.

In Japanese Patent Publications No. 2011-217820 A, No. 2013-126541 A,No. 2013-126542 A, No. 2013-126543 A and No. 2014-014383 A, variousphysical properties of the paint film are measured by using a measuringsample formed from the constituent materials of the paint film, ratherthan the actual paint film formed on the surface of the golf ball body.The measuring sample has a much greater thickness than the paint filmactually formed on the surface of the golf ball body. Thus, there is aproblem that even if the performances of the paint film are controlledbased on the physical properties of the measuring sample, the paint filmactually formed on the surface of the golf ball body may fail to exhibitthe desired performances. In addition, in the technology of JapanesePatent Publication No. 2016-123632 A, the elastic modulus of the paintfilm is directly measured on the paint film formed on the surface of thegolf ball with a scanning probe microscope in an atomic force microscopemode. However, the measured elastic modulus is much affected by thecover under the paint film and thus is considered not to be the elasticmodulus of the paint film itself.

The present invention has been achieved in view of the above problems.An object of the present invention is to provide a golf ball having goodspin performance on approach shots and good shot feeling as well asexcellent stain resistance by precisely controlling physical propertiesof a paint film actually formed on a surface of a golf ball body.

The present invention that has solved the above problems provides a golfball comprising a golf ball body and a paint film formed on a surface ofthe golf ball body, wherein the paint film is such that a linearapproximation curve obtained by a least square method has a slope in arange from 0.0015 to 0.0045 when a storage modulus (GPa) of the paintfilm in a state of being formed on the surface of the golf ball bodymeasured by the following measuring condition 1 is plotted as a verticalaxis against a measuring frequency (Hz) as a horizontal axis, and thatan elastic modulus of the paint film in the state of being formed on thesurface of the golf ball body measured by the following measuringcondition 2 ranges from 0.040 GPa to 0.600 GPa:

<Measuring Condition 1>

Measuring apparatus: “TI950 Tribo Indenter” available from Hysitron,Inc.

Indenter specification: Berkovich type

Test load (maximum indenting load): 100 μN

Frequency: 1 Hz, 10 Hz, 105 Hz

Measuring environment: 23° C., RH 50%, in the atmosphere;

<Measuring Condition 2>

Measuring apparatus: “TI950 Tribo Indenter” available from Hysitron,Inc.

Indenter specification: Berkovich type

Maximum indenting depth: 300 nm

Measuring environment: 23° C., RH 50%, in the atmosphere.

According to the present invention, a golf ball having good spinperformance on approach shots and good shot feeling as well as excellentstain resistance is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a partially cutaway cross-sectional view showing a golfball according to one embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a golf ball comprising a golf ball bodyand a paint film formed on a surface of the golf ball body, wherein thepaint film is such that a linear approximation curve obtained by a leastsquare method has a slope in a range from 0.0015 to 0.0045 when astorage modulus (GPa) of the paint film in a state of being formed onthe surface of the golf ball body measured by the following measuringcondition 1 is plotted as a vertical axis against a measuring frequency(Hz) as a horizontal axis, and that an elastic modulus of the paint filmin the state of being formed on the surface of the golf ball bodymeasured by the following measuring condition 2 ranges from 0.040 GPa to0.600 GPa:

<Measuring Condition 1>

Measuring apparatus: “TI950 Tribo Indenter” available from Hysitron,Inc.

Indenter specification: Berkovich type

Test load (maximum indenting load): 100 μN

Frequency: 1 Hz, 10 Hz, 105 Hz

Measuring environment: 23° C., RH 50%, in the atmosphere;

<Measuring Condition 2>

Measuring apparatus: “TI950 Tribo Indenter” available from Hysitron,Inc.

Indenter specification: Berkovich type

Maximum indenting depth: 300 nm

Measuring environment: 23° C., RH 50%, in the atmosphere.

In the present invention, the actual physical properties of the paintfilm can be measured highly precisely under the measuring conditions 1and 2 by using the paint film formed on the surface of the golf ballbody as an object to be directly measured.

Specifically, the measuring condition 1 is based on the followingnanoindentation method. That is, “TI950 Tribo Indenter” available fromHysitron, Inc. is used as a measuring apparatus, the measuring apparatusis set to a dynamic viscoelasticity mode, a tip of a Berkovich typeindenter (made of diamond and having a shape of triangular pyramid) isindented into the paint film which is a measuring object with a nanoloadsuch as a submilli Newton (maximum indenting load is set to 100 μN inthe measuring condition 1) to provide a nanostrain, and the dynamicviscoelasticity of the paint film is calculated based on the obtainedresponse.

In addition, the measuring condition 2 is based on the followingnanoindentation method. That is, “TI950 Tribo Indenter” available fromHysitron, Inc. is used as a measuring apparatus, the measuring apparatusis set to an indenting mode, a tip of a Berkovich type indenter (made ofdiamond and having a shape of triangular pyramid) is indented into thepaint film which is a measuring object with a nanoload such as asubmilli Newton to continuously measure an indenting load (applied load)and an indenting depth (displacement) of the indenter (maximum indentingdepth is set to 300 nm in the measuring condition 2), a relationship ofthe indenting load of the indenter against the indenting depth of theindenter is plotted to obtain a load-displacement curve, and thehardness or elastic modulus of the paint film is calculated based on theobtained load-displacement curve.

The indenting depth in the measuring conditions 1, 2 based on thenanoindentation method is only about one-tenths to one-hundredths of thethickness of the paint film, thus various physical properties of thepaint film can be accurately measured by the measuring conditions 1, 2without being affected by the golf ball body under the paint film.Accordingly, the various physical properties measured by the measuringconditions 1, 2 are considered to be the physical properties of thepaint film itself. Since the actual physical properties of the paintfilm can be measured by the measuring conditions 1, 2, the golf ballexerting the desired paint film performance can be obtained.

In the present invention, a linear approximation curve obtained by aleast square method has a slope (GPa/Hz) in a range from 0.0015 to0.0045 when a storage modulus (GPa) of the paint film in the state ofbeing formed on the surface of the golf ball body measured by the abovemeasuring condition 1 is plotted as a vertical axis against a measuringfrequency (Hz) as a horizontal axis. If the linear approximation curveof the paint film has the slope in the range from 0.0015 to 0.0045, theobtained golf ball has especially improved stain resistance.

From the viewpoint of further enhancing the stain resistance of the golfball, the slope of the linear approximation curve of the paint film ispreferably 0.0020 or more, more preferably 0.0022 or more, and even morepreferably 0.0025 or more, and is preferably 0.0040 or less, morepreferably 0.0035 or less, and even more preferably 0.0030 or less.

Specifically, each storage modulus is measured at the measuringfrequencies of 1 Hz, 10 Hz, 105 Hz (test load, i.e. maximum indentingload is set to 100 μN). The storage modulus is plotted against themeasuring frequencies of 1 Hz, 10 Hz, 105 Hz with the measuringfrequency (Hz) as the horizontal axis and the storage modulus (GPa) asthe vertical axis. The slope of the linear approximation curve iscalculated based on the obtained three plotted points.

The storage modulus of the paint film in the state of being formed onthe surface of the golf ball body at the measuring frequency of 1 Hz ispreferably 0.100 GPa or more, more preferably 0.200 GPa or more, andeven more preferably 0.300 GPa or more, and is preferably 0.850 GPa orless, more preferably 0.750 GPa or less, even more preferably 0.650 GPaor less, and most preferably 0.550 GPa or less. If the storage modulusof the paint film at the measuring frequency of 1 Hz falls within theabove range, the obtained golf ball has further enhanced spinperformance on approach shots and shot feeling while maintaining thestain resistance thereof.

The storage modulus of the paint film in the state of being formed onthe surface of the golf ball body at the measuring frequency of 10 Hz ispreferably 0.200 GPa or more, more preferably 0.300 GPa or more, andeven more preferably 0.400 GPa or more, and is preferably 1.000 GPa orless, more preferably 0.900 GPa or less, even more preferably 0.800 GPaor less, and most preferably 0.700 GPa or less. If the storage modulusof the paint film at the measuring frequency of 10 Hz falls within theabove range, the obtained golf ball has further enhanced spinperformance on approach shots and shot feeling while maintaining thestain resistance thereof.

The storage modulus of the paint film in the state of being formed onthe surface of the golf ball body at the measuring frequency of 105 Hzis preferably 0.300 GPa or more, more preferably 0.400 GPa or more, andeven more preferably 0.500 GPa or more, and is preferably 1.200 GPa orless, more preferably 1.000 GPa or less, even more preferably 0.800 GPaor less, and most preferably 0.700 GPa or less. If the storage modulusof the paint film at the measuring frequency of 105 Hz falls within theabove range, the obtained golf ball has further enhanced spinperformance on approach shots and shot feeling while maintaining thestain resistance thereof.

In the present invention, the elastic modulus of the paint film in thestate of being formed on the surface of the golf ball body measured bythe above measuring condition 2 ranges from 0.040 GPa to 0.600 GPa. Ifthe elastic modulus of the paint film ranges from 0.040 GPa to 0.600GPa, the obtained golf ball has further enhanced spin performance onapproach shots and shot feeling while maintaining the stain resistancethereof.

From the viewpoint of further enhancing the spin performance on approachshots and shot feeling, the elastic modulus of the paint film in thestate of being formed on the surface of the golf ball body is preferably0.060 GPa or more, more preferably 0.100 GPa or more, and even morepreferably 0.150 GPa or more, and is preferably 0.500 GPa or less, morepreferably 0.400 GPa or less, and even more preferably 0.300 GPa orless.

The hardness of the paint film in the state of being formed on thesurface of the golf ball body measured by the measuring condition 2 ispreferably 0.001 GPa or more, more preferably 0.002 GPa or more, andeven more preferably 0.003 GPa or more, and is preferably 0.020 GPa orless, more preferably 0.015 GPa or less, even more preferably 0.010 GPaor less, and most preferably 0.005 GPa or less. If the hardness of thepaint film measured by the measuring condition 2 falls within the aboverange, the obtained golf ball has further enhanced spin performance onapproach shots and shot feeling while maintaining the stain resistancethereof. In addition, the paint film has better durability. It is notedthat the hardness of the paint film is a hardness calculated from theindenting load F (i.e. load applied at the maximum displacement of 300nm) when the indenter is indented into the paint film in a depth of 300nm by the measuring condition 2.

The 10% elastic modulus of the paint film is preferably 20 kgf/cm² (2.0MPa) or more, more preferably 30 kgf/cm² (2.9 MPa) or more, and evenmore preferably 40 kgf/cm² (3.9 MPa) or more, and is preferably 180kgf/cm² (17.6 MPa) or less, more preferably 150 kgf/cm² (14.7 MPa) orless, and even more preferably 100 kgf/cm² (9.8 MPa) or less. If 10%elastic modulus of the paint film is 20 kgf/cm² or more, the paint filmhas better stain resistance, and if 10% elastic modulus of the paintfilm is 180 kgf/cm² or less, the spin performance on approach shots isfurther enhanced. It is noted that the 10% elastic modulus is measuredby the method described later.

The paint film may have a single-layered construction (including thecase where the same paint is applied for a plurality of times) or amultiple-layered construction composed of at least two layers (the casewhere two layers adjacent to each other are formed from paints differentfrom each other), and the paint film having the single-layeredconstruction (including the case where the same paint is applied forseveral times) is preferred from the viewpoint of more preciselymeasuring the physical properties of the paint film by the measuringconditions 1, and 2.

The thickness of the paint film is preferably 5 μm or more, morepreferably 10 μm or more, and even more preferably 15 μm or more. If thethickness of the paint film is less than 5 μm, the paint film may beeasy to wear off due to the continued use of the golf ball. If thethickness of the paint film is great, the spin rate on approach shotsincreases. In addition, the thickness of the paint film is preferably 50μm or less, more preferably 45 μm or less, and even more preferably 40μm or less. If the thickness of the paint film exceeds 50 μm, the dimpleeffect is reduced and thus the flight performance of the golf ball maybe lowered. The thickness of the paint film can be obtained, forexample, by measuring a cross section of the golf ball with a microscope(VHX-1000 available from Keyence Corporation). It is noted that thethickness of the paint film is a total thickness of the formed paintfilm.

The above mentioned various physical properties of the paint film can becontrolled by appropriately choosing the type of the base resinconstituting the paint film, for examples, the type or amount of thecomponents blended in the base resin.

Examples of the base resin constituting the paint film includepolyurethane, epoxy resin, acrylic resin, vinyl acetate resin, andpolyester. Among them, the polyurethane is preferred. If the base resinconstituting the paint film is the polyurethane, various physicalproperties of the paint film can be easily obtained by adjusting theamount of the polyol composition or the polyisocyanate composition, orthe mixing ratio thereof.

(Polyurethane Paint)

The base resin constituting the paint film is preferably a polyurethaneformed from a paint containing a polyol composition and a polyisocyanatecomposition. The reaction between the polyol composition and thepolyisocyanate composition forms the polyurethane. As the paint, aso-called curing type urethane paint containing a polyol as a basematerial and a polyisocyanate as a curing agent can be exemplified.

(Polyol Composition)

The polyol composition contains a polyol compound. Examples of thepolyol compound include a compound having two or more hydroxyl groups inthe molecule. The polyol compound may be used solely or as a mixture ofat least two of them.

Examples of the polyol compound include a low molecular weight polyolhaving a molecular weight of less than 500, and a high molecular weightpolyol having a number average molecular weight of 500 or more. Examplesof the low molecular weight polyol include a diol such as ethyleneglycol, diethylene glycol, triethylene glycol, 1,3-butanediol,1,4-butanediol, neopentyl glycol, and 1,6-hexanediol; and a triol suchas glycerin, trimethylolpropane, and hexanetriol. Examples of the highmolecular weight polyol include a polyether polyol, a polyester polyol,a polycaprolactone polyol, a polycarbonate polyol, a urethane polyol,and an acrylic polyol.

Examples of the polyether polyol include polyoxyethylene glycol (PEG),polyoxypropylene glycol (PPG), and polyoxytetramethylene glycol (PTMG).Examples of the polyester polyol include polyethylene adipate (PEA),polybutylene adipate (PBA), and polyhexamethylene adipate (PHMA).Examples of the polycaprolactone polyol include poly-ε-caprolactone(PCL). Examples of the polycarbonate polyol include polyhexamethylenecarbonate.

The urethane polyol is a compound having a plurality of urethane bondsin the molecule, and having two or more hydroxyl groups in one molecule.Examples of the urethane polyol include a urethane prepolymer obtainedby a reaction between a polyol component and a polyisocyanate component,under a condition that the amount of hydroxyl groups in the polyolcomponent is excessive to the amount of isocyanate groups in thepolyisocyanate component.

Examples of the polyol component constituting the urethane polyolinclude a diol component such as a polyether diol, a polyester diol, apolycaprolactone diol and a polycarbonate diol. The polyether diol ispreferred. Examples of the polyether diol include polyoxyethyleneglycol, polyoxypropylene glycol, and polyoxytetramethylene glycol. Amongthem, the polyoxytetramethylene glycol is preferred.

The number average molecular weight of the polyether diol is preferably550 or more, more preferably 600 or more, and even more preferably 650or more, and is preferably 3000 or less, more preferably 2500 or less,and even more preferably 2000 or less. If the number average molecularweight of the polyether diol is 550 or more, the distance betweencrosslinking points in the paint film becomes long, the paint filmbecomes soft, and thus the golf ball has enhanced spin performance onapproach shots and shot feeling. If the number average molecular weightof the polyether diol is 3,000 or less, the distance betweencrosslinking points in the paint film does not become excessively long,and thus the stain resistance of the paint film becomes better. It isnoted that the number average molecular weight of the polyol componentcan be measured, for example, by gel permeation chromatography (GPC),using polystyrene as a standard material, tetrahydrofuran as an eluate,and an organic solvent system GPC column (e.g. “Shodex (registeredtrademark) KF series” available from Showa Denko K.K.) as a column.

The polyol component may further contain a low molecular weight polyolhaving a molecular weight of less than 500. Examples of the lowmolecular weight polyol include a diol such as ethylene glycol,diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol,neopentyl glycol, and 1,6-hexanediol; and a triol such as glycerin,trimethylolpropane, and hexanetriol. The low molecular weight polyol maybe used solely or as a mixture of at least two of them.

The polyol component constituting the urethane polyol preferablyincludes the triol component and the diol component. As the triolcomponent, trimethylolpropane is preferred. The mixing ratio (triolcomponent/diol component) of the triol component to the diol componentis preferably 0.2 or more, more preferably 0.3 or more, and even morepreferably 0.5 or more, and is preferably 6.0 or less, more preferably4.0 or less, even more preferably 2.0 or less, and most preferably 1.0or less in a molar ratio. If the polyol component constituting theurethane polyol includes the triol component and the diol component inthe mixing ratio falling within the above range, the golf ball hasfurther enhanced spin performance on approach shots as well as betterstain resistance and durability.

The polyisocyanate component constituting the urethane polyol is notparticularly limited, as long as it has two or more isocyanate groups.Examples of the polyisocyanate component include an aromaticpolyisocyanate such as 2,4-tolylene diisocyanate, 2,6-tolylenediisocyanate, a mixture of 2,4-tolylene diisocyanate and 2,6-tolylenediisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI),1,5-naphthylene diisocyanate (NDI), 3,3′-bitolylene-4,4′-diisocyanate(TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate(TMXDI), and para-phenylene diisocyanate (PPDI); and an alicyclicpolyisocyanate or aliphatic polyisocyanate such as4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrogenated xylylenediisocyanate (H₆XDI), hexamethylene diisocyanate (HDI), isophoronediisocyanate (IPDI), and norbornene diisocyanate (NBDI). Thesepolyisocyanates may be used solely, or at least two of them may be usedin combination.

The amount of the polyether diol in the urethane polyol is preferably 50mass % or more, more preferably 60 mass % or more, and even morepreferably 65 mass % or more. The polyether diol forms a soft segment inthe paint film. Therefore, if the amount of the polyether diol is 50mass % or more, the obtained golf ball has further enhanced spinperformance and shot feeling.

The weight average molecular weight of the urethane polyol is preferably3,000 or more, more preferably 4,000 or more, and even more preferably4,500 or more, and is preferably 10,000 or less, more preferably 8,000or less, and even more preferably 6,000 or less. If the weight averagemolecular weight of the urethane polyol is 3,000 or more, the distancebetween crosslinking points in the paint film becomes long, the paintfilm becomes soft, and thus the golf ball has enhanced spin performanceon approach shots and shot feeling. If the weight average molecularweight of the urethane polyol is 10,000 or less, the distance betweencrosslinking points in the paint film does not become excessively long,and thus the stain resistance of the paint film becomes better.

The hydroxyl value of the urethane polyol is preferably 20 mg KOH/g ormore, more preferably 30 mg KOH/g or more, and even more preferably 50mg KOH/g or more, and is preferably 100 mg KOH/g or less, morepreferably 90 mg KOH/g or less, and even more preferably 80 mg KOH/g orless. It is noted that the hydroxyl value can be measured by, forexample, an acetylization method, in accordance with JIS K 1557-1.

The polyol composition preferably contains the urethane polyol as thepolyol compound. The amount of the urethane polyol in the polyolcompound of the polyol composition is preferably 60 mass % or more, morepreferably 70 mass % or more, and even more preferably 80 mass % ormore. In addition, it is most preferred that the polyol compound of thepolyol composition consists of the urethane polyol.

(Polyisocyanate Composition)

Next, the polyisocyanate composition will be explained. Thepolyisocyanate composition contains a polyisocyanate compound. Examplesof the polyisocyanate compound include a compound having two or moreisocyanate groups.

Examples of the polyisocyanate compound include an aromatic diisocyanatesuch as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, a mixtureof 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate (TDI),4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate(NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate(XDI), tetramethylxylylene diisocyanate (TMXDI), and para-phenylenediisocyanate (PPDI); an alicyclic diisocyanate or aliphatic diisocyanatesuch as 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrogenatedxylylene diisocyanate (H₆XDI), hexamethylene diisocyanate (HDI),isophorone diisocyanate (IPDI), and norbornene diisocyanate (NBDI); anda triisocyanate such as an allophanate-modified product, abiuret-modified product, an isocyanurate-modified product and an adductproduct of the above diisocyanates. The polyisocyanate may be usedsolely, or at least two of them may be used in combination.

The allophanate-modified product is, for example, a triisocyanateobtained by further reacting a diisocyanate with a urethane bond formedthrough a reaction between a diisocyanate and a low molecular weightdiol. The adduct product is a triisocyanate obtained through a reactionbetween a diisocyanate and a low molecular weight triol such astrimethylolpropane or glycerin. The biuret-modified product is, forexample, a triisocyanate having a biuret bond represented by thefollowing chemical formula (1). The isocyanurate-modified product of thediisocyanate is, for example, a triisocyanate represented by thefollowing chemical formula (2).

In the chemical formulae (1) and (2), R represents a residue whereisocyanate groups are removed from the diisocyanate.

As the triisocyanate, at least one member selected from the groupconsisting of an isocyanurate-modified product of hexamethylenediisocyanate, a biuret-modified product of hexamethylene diisocyanateand an isocyanurate-modified product of isophorone diisocyanate ispreferred, and the combined use of these modified products is morepreferred. In particular, in case of using the biuret-modified productof hexamethylene diisocyanate and the isocyanurate-modified product ofhexamethylene diisocyanate in combination, a mixing ratio(biuret-modified product/isocyanurate-modified product) thereofpreferably ranges from 0.5 to 2.0, more preferably ranges from 0.8 to1.5, and even more preferably ranges from 0.9 to 1.4 in a mass ratio. Inaddition, in case of using the modified product of hexamethylenediisocyanate (biuret-modified product and/or isocyanurate-modifiedproduct) and the isocyanurate-modified product of isophoronediisocyanate in combination, a mixing ratio (the modified product ofhexamethylene diisocyanate/isocyanurate-modified product of isophoronediisocyanate) thereof preferably ranges from 0.5 to 3.0, more preferablyranges from 0.8 to 2.5, and even more preferably ranges from 1.0 to 2.0in a mass ratio.

The polyisocyanate composition preferably contains the triisocyanatecompound as the polyisocyanate compound. The amount of the triisocyanatecompound in the polyisocyanate compound of the polyisocyanatecomposition is preferably 60 mass % or more, more preferably 70 mass %or more, and even more preferably 80 mass % or more. In addition, it ismost preferred that the polyisocyanate compound of the polyisocyanatecomposition consists of the triisocyanate compound.

The amount of the isocyanate group (NCO %) in the polyisocyanatecompound contained in the polyisocyanate composition is preferably 0.5mass % or more, more preferably 1 mass % or more, and even morepreferably 2 mass % or more, and is preferably 45 mass % or less, morepreferably 40 mass % or less, and even more preferably 35 mass % orless. It is noted that the amount of the isocyanate group (NCO %) in thepolyisocyanate can be defined by the following expression.

NCO (%)=100×[mole number of isocyanate groups in thepolyisocyanate×42(molecular weight of NCO)]/[total mass(g) of thepolyisocyanate]

Specific examples of the polyisocyanate include Bumock D-800, BumockDN-950, and Bumock DN-955 available from DIC corporation; DesmodurZ4470, Desmodur N75MPA/X, Desmodur N3300, Desmodur L75 (C), and SumidurE21-1 available from Sumika Bayer Urethane Co., Ltd.; Coronate HX andCoronate HK available from Nippon Polyurethane Industry Co., Ltd.;Duranate 24A-100, Duranate 21S-75E, Duranate TPA-100, and DuranteTKA-100 available from Asahi Kasei Chemicals Corporation; and VESTANATT1890 available from Degussa.

In the curing reaction of the curing type paint composition, the massratio (polyol composition/polyisocyanate composition) of the polyolcomposition to the polyisocyanate composition is preferably 3.5 or more,more preferably 4.0 or more, even more preferably 5.0 or more, and mostpreferably 6.0 or more, and is preferably 10.0 or less, more preferably9.0 or less, and even more preferably 8.5 or less. If the mass ratio(polyol composition/polyisocyanate composition) of the curing type paintcomposition falls within the above range, the above mentioned variousphysical properties of the obtained paint film are easily satisfied, andthus a golf ball having good spin performance on approach shots and goodshot feeling as well as excellent stain resistance is easily obtained.On the other hand, if the mass ratio is less than 3.5, the paint filmbecomes so hard that the obtained golf ball may have dissatisfactoryspin performance on approach shots and shot feeling. In addition, if themass ratio is more than 10.0, the paint film becomes so soft that theobtained golf ball may have dissatisfactory stain resistance.

In the curing reaction of the curing type paint composition, the molarratio (NCO group/OH group) of the isocyanate group (NCO group) in thecuring agent to the hydroxyl group (OH group) in the base material ispreferably 0.15 or more, more preferably 0.18 or more, even morepreferably 0.20 or more, and most preferably 0.22 or more, and ispreferably 1.20 or less, more preferably 1.10 or less, and even morepreferably 1.00 or less. If the molar ratio (NCO group/OH group) of thecuring type paint composition falls within the above range, the abovementioned various physical properties of the obtained paint film areeasily satisfied, and thus a golf ball having good spin performance onapproach shots and good shot feeling as well as excellent stainresistance is easily obtained. On the other hand, if the molar ratio isless than 0.15, the obtained paint film becomes so soft thatdefectiveness may occur during the manufacturing process. In addition,if the molar ratio is more than 1.20, the obtained paint film becomes sohard that the obtained golf ball may have inferior spin performance.

The paint may be either a waterborne paint mainly containing water as adispersion medium or a solvent-based paint containing an organic solventas a dispersion medium, and the solvent-based paint is preferred. Incase of the solvent-based paint, preferable examples of the solventinclude toluene, isopropyl alcohol, xylene, methyl ethyl ketone, methylethyl isobutyl ketone, ethylene glycol monomethyl ether, ethylbenzene,propylene glycol monomethyl ether, isobutyl alcohol, ethyl acetate, andbutyl acetate. It is noted that the solvent may be added into either thepolyol composition or the polyisocyanate composition, and from theviewpoint of uniformly performing the curing reaction, the solvent ispreferably added into both the polyol composition and the polyisocyanatecomposition.

In the curing reaction, a publicly known catalyst may be used. Examplesof the catalyst include a monoamine such as triethylamine andN,N-dimethylcyclohexylamine; a polyamine such asN,N,N′,N′-tetramethylethylene diamine andN,N,N′,N″,N″-pentamethyldiethylene triamine; a cyclic diamine such as1,8-diazabicyclo-[5.4.0]-7-undecene (DBU) and triethylenediamine; and atin-based catalyst such as dibutyl tin dilaurylate and dibutyl tindiacetate. These catalysts may be used solely, or at least two of themmay be used in combination. Among them, the tin-based catalyst such asdibutyl tin dilaurylate and dibutyl tin diacetate is preferable, anddibutyl tin dilaurylate is particularly preferable.

If necessary, the paint may further contain an additive generallycontained in a golf ball paint, such as a filler, an ultravioletabsorber, an antioxidant, a light stabilizer, a fluorescent brightener,an anti-blocking agent, a leveling agent, a slip agent, and a viscositymodifier.

The method of applying the curing type paint of the present invention isnot particularly limited, and a conventionally known method such as aspray coating method or an electrostatic coating method may be employed.

In case of spray coating using an air gun, the polyol composition andthe polyisocyanate composition may be fed with respective pumps andcontinuously mixed with a line mixer located in the stream line justbefore the air gun, and the obtained mixture is subjected to spraycoating. Alternatively, the polyol composition and the polyisocyanatecomposition may be subjected to spray coating separately by using an airspray system provided with a mixing ratio controlling device. The paintapplication may be conducted by spray coating one time or oversprayingseveral times.

The curing type paint applied to the golf ball body may be dried, forexample, at a temperature ranging from 30° C. to 70° C. for 1 hour to 24hours to form the paint film.

The golf ball according to the present invention is not particularlylimited, as long as it comprises a golf ball body and a paint filmformed on a surface of the golf ball body. The construction of the golfball body is not particularly limited, and may be a one-piece golf ball;a two-piece golf ball; a three-piece golf ball; a four-piece golf ball;a multi-piece golf ball comprising five or more pieces; or a wound golfball. The present invention can be applied appropriately to any one ofthe above golf ball bodies.

The FIGURE is a partially cutaway cross-sectional view of a golf ball 1according to one embodiment of the present invention (schematicdrawing). The golf ball 1 comprises a spherical core 2, a cover 3covering the spherical core 2, and a paint film 4 formed on a surface ofthe cover 3. A plurality of dimples 31 are formed on the surface of thecover 3. Other portions than the dimples 31 on the surface of the cover3 are land 32.

Next, the one-piece golf ball body and the core used in a wound golfball, two-piece golf ball and multi-piece golf ball will be explained.

The core may be either a single-layered construction, or a multi-layeredconstruction composed of at least two layers, without any limitation.The core preferably has a single-layered construction. Unlike themulti-layered core, the single-layered core does not have an energy lossat the interface of the multi-layered construction when being hit, andthus has better resilience. The core preferably has a spherical shape.

The one-piece golf ball body and the core may be formed by using aconventional rubber composition (hereinafter, sometimes simply referredto as “core rubber composition”). For example, the one-piece golf ballbody and the core may be formed by heat pressing a rubber compositioncontaining a base rubber, a co-crosslinking agent, and a crosslinkinginitiator.

As the base rubber, particularly preferred is a high cis-polybutadienehaving a cis-bond which is beneficial to the resilience in an amount of40 mass % or more, preferably 70 mass % or more, and more preferably 90mass % or more. As the co-crosslinking agent, an α,β-unsaturatedcarboxylic acid having 3 to 8 carbon atoms or a metal salt thereof ispreferred, and acrylic acid metal salt and methacrylic acid metal saltare more preferred. As the metal constituting the metal salt, zinc,magnesium, calcium, aluminum and sodium are preferred, and zinc is morepreferred. The amount of the co-crosslinking agent is preferably 20parts by mass or more and 50 parts by mass or less with respect to 100parts by mass of the base rubber. When the α,β-unsaturated carboxylicacid having 3 to 8 carbon atoms is used as the co-crosslinking agent, ametal compound is preferably blended. When the metal salt of theα,β-unsaturated carboxylic acid having 3 to 8 carbon atoms is used asthe co-crosslinking agent, the metal compound may be blended. As thecrosslinking initiator, an organic peroxide is preferably used. Specificexamples of the organic peroxide include dicumyl peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,5-dimethyl-2,5-di(t-butylperoxy) hexane and di-t-butyl peroxide. Amongthem, dicumyl peroxide is preferably used. The amount of thecrosslinking initiator is preferably 0.2 part by mass or more, morepreferably 0.3 part by mass or more, and is preferably 3 parts by massor less, more preferably 2 parts by mass or less, with respect to 100parts by mass of the base rubber.

The core rubber composition may further contain an organic sulfurcompound. Preferable examples of the organic sulfur compound includediphenyl disulfides (e.g. diphenyl disulfides, bis(pentabromophenyl)disulfides), thiophenols, and thionaphthols (e.g. 2-thionaphthol). Theamount of the organic sulfur compound is preferably 0.1 part by mass ormore, more preferably 0.3 part by mass or more, and is preferably 5.0parts by mass or less, more preferably 3.0 parts by mass or less, withrespect to 100 parts by mass of the base rubber. The core rubbercomposition may further contain a carboxylic acid and/or a salt thereof.As the carboxylic acid and/or the salt thereof, a carboxylic acid having1 to 30 carbon atoms and/or a salt thereof is preferred. As thecarboxylic acid, either an aliphatic carboxylic acid or an aromaticcarboxylic acid (such as benzoic acid) may be used. The amount of thecarboxylic acid and/or the salt thereof is 1 part by mass or more and 40parts by mass or less with respect to 100 parts by mass of the baserubber.

The core rubber composition may further contain a weight adjusting agentsuch as zinc oxide and barium sulfate, an antioxidant, a colored powder,or the like appropriately, in addition to the base rubber, theco-crosslinking agent, the crosslinking initiator and the organic sulfurcompound.

Conditions for molding the core rubber composition by a heat pressingmethod may be set appropriately in accordance with the formulation ofthe core rubber composition. Generally, it is preferred that the corerubber composition is heated at 130° C. to 200° C. for 10 to 60 minutes,or alternatively the core rubber composition is subjected to a two-stepheating, i.e. the core rubber composition is heated at 130° C. to 150°C. for 20 to 40 minutes and then heated at 160° C. to 180° C. for 5 to15 minutes.

The hardness difference (Hs−Ho) between the surface hardness Hs of thecore and the center hardness Ho of the core is preferably 10 or more,more preferably 15 or more, and even more preferably 20 or more in ShoreC hardness.

If the hardness difference (Hs−Ho) is 10 or more, the spin rate ondriver shots is further lowered and thus the flight distance on drivershots is greater. In addition, the hardness difference (Hs−Ho) ispreferably 50 or less, more preferably 45 or less, even more preferably40 or less, and most preferably 35 or less in Shore C hardness. If thehardness difference (Hs−Ho) is 50 or less, the golf ball has betterdurability.

The center hardness Ho of the core is preferably 40 or more, morepreferably 45 or more, and even more preferably 50 or more in Shore Chardness. If the center hardness Ho of the core is 40 or more, the golfball has better resilience and thus the flight distance thereof ondriver shots is greater. In addition, the center hardness Ho of the coreis preferably 80 or less, more preferably 75 or less, and even morepreferably 70 or less in Shore C hardness. If the center hardness Ho ofthe core is 80 or less, the golf ball has better shot feeling.

The surface hardness Hs of the core is preferably 60 or more, morepreferably 65 or more, and even more preferably 70 or more in Shore Chardness. If the surface hardness Hs of the core is 60 or more, the golfball has better resilience and thus the flight distance thereof ondriver shots is greater. In addition, the surface hardness Hs of thecore is preferably 100 or less, more preferably 95 or less, and evenmore preferably 90 or less in Shore C hardness. If the surface hardnessHs of the core is 100 or less, the core does not become too hard andthus the durability thereof is better.

The diameter of the core is preferably 37.0 mm or more, more preferably37.5 mm or more, and even more preferably 38.5 mm or more. If the corehas the diameter of 37.0 mm or more, the resilience thereof is better.The upper limit of the diameter of the core is preferably 40.5 mm orless, more preferably 40.0 mm or less, and even more preferably 39.8 mmor less, without any limitation.

When the core has a diameter in a range from 37.0 mm to 40.5 mm, thecompression deformation amount of the core (shrinking amount of the corealong the compression direction) when applying a load from 98 N as aninitial load to 1275 N as a final load to the core is preferably 2.5 mmor more, more preferably 3.0 mm or more, and is preferably 4.5 mm orless, more preferably 4.0 mm or less. If the compression deformationamount is 2.5 mm or more, the shot feeling is better, and if thecompression deformation amount is 4.5 mm or less, the resilience isbetter.

The golf ball body preferably has a core and a cover. Herein, the covermeans a layer disposed on the outermost side of the golf ball body (alsoreferred to as “outermost cover”).

The cover composition constituting the cover preferably contains a resincomponent. Examples of the resin component include various resins suchas an ionomer resin, a polyester resin and a polyamide resin, athermoplastic polyurethane elastomer having a trade name of “Elastollan(registered trademark)” available from BASF Japan Ltd., a thermoplasticpolyamide elastomer having a trade name of “Pebax (registeredtrademark)” available from Arkema K. K., a thermoplastic polyesterelastomer having a trade name of “Hytrel (registered trademark)”available from Du Pont-Toray Co., Ltd., and a thermoplastic styreneelastomer having a trade name of “Rabalon (registered trademark)”available from Mitsubishi Chemical Corporation.

Examples of the ionomer resin include a product obtained by neutralizingat least a part of carboxyl groups of a binary copolymer composed of anolefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atomswith a metal ion; a product obtained by neutralizing at least a part ofcarboxyl groups of a ternary copolymer composed of an olefin, anα,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and anα,β-unsaturated carboxylic acid ester with a metal ion; and a mixturethereof. The olefin is preferably an olefin having 2 to 8 carbon atoms.Examples of the olefin include ethylene, propylene, butene, pentene,hexene, heptene and octene, and ethylene is particularly preferred.Examples of the α,β-unsaturated carboxylic acid having 3 to 8 carbonatoms include acrylic acid, methacrylic acid, fumaric acid, maleic acidand crotonic acid, and acrylic acid or methacrylic acid is particularlypreferred. In addition, examples of the α,β-unsaturated carboxylic acidester include methyl ester, ethyl ester, propyl ester, n-butyl ester,isobutyl ester of acrylic acid, methacrylic acid, fumaric acid andmaleic acid, and acrylic acid ester or methacrylic acid ester isparticularly preferred. Among them, as the ionomer resin, a metalion-neutralized product of ethylene-(meth)acrylic acid binary copolymeror a metal ion-neutralized product of ethylene-(meth)acrylicacid-(meth)acrylic acid ester ternary copolymer is preferred.

Specific examples of the ionomer resin include “Himilan (registeredtrademark) (e.g. Himilan 1555 (Na), Himilan 1557 (Zn), Himilan 1605(Na), Himilan 1706 (Zn), Himilan 1707 (Na), Himilan AM3711 (Mg), HimilanAM7337 (Na), Himilan AM7329 (Zn); and a ternary copolymer ionomer resinsuch as Himilan 1856 (Na) and Himilan 1855 (Zn))” available fromMitsui-Du Pont Polychemicals Co., Ltd.

Examples of the ionomer resin available from E.I. du Pont de Nemours andCompany include “Surlyn (registered trademark) (e.g. Surlyn 8945 (Na),Surlyn 9945 (Zn), Surlyn 8140 (Na), Surlyn 8150 (Na), Surlyn 9120 (Zn),Surlyn 9150 (Zn), Surlyn 6910 (Mg), Surlyn 6120 (Mg), Surlyn 7930 (Li),Surlyn 7940 (Li), Surlyn AD8546 (Li); and a ternary copolymer ionomerresin such as Surlyn 8120 (Na), Surlyn 8320 (Na), Surlyn 9320 (Zn),Surlyn 6320 (Mg), HPF1000 (Mg), and HPF2000 (Mg))”.

Examples of the ionomer resin available from ExxonMobil ChemicalCorporation include “Iotek (registered trademark) (e.g. Iotek 8000 (Na),Iotek 8030 (Na), Iotek 7010 (Zn), Iotek 7030 (Zn); and a ternarycopolymer ionomer resin such as Iotek 7510 (Zn), and Iotek 7520 (Zn))”.

It should be noted that Na, Zn, Li, Mg and the like described in theparentheses after the trade names of the ionomer resins indicate metaltypes of neutralizing metal ions of the ionomer resins. The ionomerresin may be used solely or as a mixture of at least two of them.

The cover composition preferably contains a thermoplastic polyurethaneelastomer or an ionomer resin as the resin component. The amount of thepolyurethane or ionomer resin in the resin component of the covercomposition is preferably 40 mass % or more, more preferably 50 mass %or more, even more preferably 60 mass % or more, and most preferably 70mass % or more. In addition, it is also preferred that the resincomponent of the cover composition consists of the thermoplasticpolyurethane elastomer or the ionomer resin. It is noted that when theionomer resin is used, a thermoplastic styrene elastomer is preferablyused in combination. In this case, the mass ratio of the ionomer resinto the thermoplastic styrene elastomer (ionomer resin/thermoplasticstyrene elastomer) is preferably 40/60 or more, more preferably 45/55 ormore, and even more preferably 50/50 or more, and is preferably 80/20 orless, more preferably 70/30 or less, and even more preferably 60/40 orless. If the mass ratio of the ionomer resin to the thermoplasticstyrene elastomer in the resin component of the cover composition fallswithin the above range, a synergistic effect with the spin performanceimprovement effect on approach shots based on the paint film accordingto the present invention is achieved, and thus the obtained golf ballhas further improved spin performance on approach shots.

In addition to the above-described resin component, the covercomposition may further contain a pigment component such as a whitepigment (e.g. titanium oxide), a blue pigment (e.g. ultramarine blue)and a red pigment, a weight adjusting agent such as zinc oxide, calciumcarbonate and barium sulfate, a dispersant, an antioxidant, anultraviolet absorber, a light stabilizer, a fluorescent material orfluorescent brightener, unless they impair the performance of the cover.

Examples of the method for molding the cover composition into the coverinclude a method which comprises injection molding the cover compositiondirectly onto the spherical body; and a method which comprises moldingthe cover composition into a hollow shell, covering the spherical bodywith a plurality of the hollow shells and performing compression molding(preferably a method which comprises molding the cover composition intoa hollow half-shell, covering the spherical body with two of thehalf-shells and performing compression molding).

The concave portions called “dimple” are usually formed on the surfaceof the cover when molding the cover. The total number of the dimplesformed on the cover is preferably 200 or more and 500 or less. If thetotal number of the dimples is less than 200, the dimple effect ishardly obtained. In addition, if the total number of the dimples exceeds500, the dimple effect is hardly obtained because the size of therespective dimple is small. The shape (shape in a plan view) of thedimples formed on the cover includes, without any limitation, a circle;a polygonal shape such as a roughly triangular shape, a roughlyquadrangular shape, a roughly pentagonal shape and a roughly hexagonalshape; and other irregular shape. These shapes may be employed solely,or at least two of them may be employed in combination.

It is preferred that the hardness of the cover is appropriately set inaccordance with the desired performance of the golf ball. For example,in case of a so-called distance golf ball focusing on the flightdistance, the cover preferably has a hardness of 50 or more, morepreferably 55 or more in shore D hardness, and preferably has a hardnessof 80 or less, more preferably 70 or less in shore D hardness. If thecover has the hardness of 50 or more, the obtained golf ball travels agreater flight distance on driver shots. In addition, if the cover hasthe hardness of 80 or less, the obtained golf ball has more excellentdurability. Further, in case of a so-called spin golf ball focusing oncontrollability, the cover preferably has a hardness of less than 50,more preferably 45 or less, and even more preferably 40 or less in ShoreD hardness, and preferably has a hardness of 20 or more, more preferably23 or more, and even more preferably 25 or more in Shore D hardness. Ifthe cover has the hardness of less than 50, the spin rate on approachshots becomes higher and thus the obtained golf ball has more excellentcontrollability. In addition, if the cover has the hardness of 20 ormore, the abrasion resistance is enhanced. It is noted that the hardnessof the cover is a slab hardness of the cover composition molded into asheet shape.

The thickness of the cover is preferably 0.3 mm or more, more preferably0.4 mm or more, and even more preferably 0.5 mm or more, and ispreferably 3.0 mm or less, more preferably 2.5 mm or less, and even morepreferably 2.3 mm or less. If the thickness of the cover is 0.3 mm ormore, the golf ball has better shot feeling as well as betterdurability. In addition, if the thickness of the cover is 3.0 mm orless, the resilience of the golf ball can be maintained.

The golf ball body according to the present invention may comprise atleast one intermediate layer between the core and the cover. It is notedthat the intermediate layer is sometimes referred to as an inner coveror outer core, depending on the construction of the golf ball.

The intermediate layer composition constituting the intermediate layerpreferably contains a resin component. Examples of the resin componentinclude a thermoplastic resin such as an ionomer resin, a polyurethaneresin, a polyamide resin, and polyethylene; a thermoplastic elastomersuch as a styrene elastomer, a polyolefin elastomer, a polyurethaneelastomer, and a polyester elastomer; and a cured product of a rubbercomposition. Among them, the ionomer resin is preferred. Preferableexamples of the ionomer resin include the ionomer resins listed in theresin components used in the cover composition. The intermediate layermay further contain a weight adjusting agent such as barium sulfate andtungsten, an antioxidant, and a pigment.

Examples of the method for molding the intermediate layer compositioninto the intermediate layer include a method which comprises injectionmolding the intermediate layer composition directly onto the core; and amethod which comprises molding the intermediate layer composition into ahollow shell, covering the core with a plurality of the hollow shellsand performing compression molding (preferably a method which comprisesmolding the intermediate layer composition into a hollow half-shell,covering the core with two of the half-shells and performing compressionmolding).

The hardness of the intermediate layer is preferably 50 or more, morepreferably 55 or more, and is preferably 80 or less, more preferably 70or less in Shore D hardness. If the hardness of the intermediate layeris 50 or more, the obtained golf ball travels a greater flight distanceon driver shots, and shows a further increased spin rate on approachshots and hence more excellent controllability. In addition, if thehardness of the intermediate layer is 80 or less, the obtained golf ballhas better shot feeling and durability. It is noted that the hardness ofthe intermediate layer is a slab hardness of the intermediate layercomposition molded into a sheet shape.

It is preferred that there is a hardness difference between theintermediate layer and the cover. The hardness difference (intermediatelayer-cover) between the intermediate layer and the cover is preferably10 or more, more preferably 15 or more, even more preferably 20 or more,and most preferably 25 or more, and is preferably 60 or less, morepreferably 50 or less, and even more preferably 40 or less in Shore Dhardness. If the hardness difference between the intermediate layer andthe cover falls within the above range, a synergistic effect with thespin performance improvement effect on approach shots based on the paintfilm according to the present invention is achieved, and thus theobtained golf ball has extremely improved spin performance on approachshots. In addition, the obtained golf ball exhibits especially improvedshot feeling as well.

The Shore D hardness ratio (intermediate layer/cover) of theintermediate layer to the cover is preferably 1.1 or more, morepreferably 1.2 or more, even more preferably 1.3 or more, and mostpreferably 1.5 or more, and is preferably 5 or less, more preferably 4or less, and even more preferably 3 or less. If the Shore D hardnessratio of the intermediate layer to the cover falls within the aboverange, a synergistic effect with the spin performance improvement effecton approach shots based on the paint film according to the presentinvention is achieved, and thus the obtained golf ball has extremelyimproved spin performance on approach shots. In addition, the obtainedgolf ball exhibits especially improved shot feeling as well.

The thickness of the intermediate layer is preferably 0.3 mm or more,more preferably 0.4 mm or more, and even more preferably 0.5 mm or more,and is preferably 4.0 mm or less, more preferably 3.0 mm or less, evenmore preferably 2.5 mm or less, and most preferably 2.0 mm or less. Ifthe thickness of the intermediate layer is 0.3 mm or more, theintermediate layer is easily molded and the obtained golf ball hasbetter durability. In addition, if the thickness of the intermediatelayer is 4.0 mm or less, the obtained golf ball has better resilienceand shot feeling. It is noted that when the intermediate layer has aplurality of layers, it is preferred that the total thickness of theintermediate layers falls within the above range.

The golf ball body having the cover formed thereon is ejected from themold, and is preferably subjected to surface treatments such asdeburring, cleaning and sandblast where necessary. In addition, ifdesired, a mark may be formed.

The golf ball according to the present invention preferably has adiameter ranging from 40 mm to 45 mm. In light of satisfying theregulation of US Golf Association (USGA), the diameter is preferably42.67 mm or more. In light of prevention of air resistance, the diameteris preferably 44 mm or less, more preferably 42.80 mm or less. The golfball preferably has a mass of 40 g or more and 50 g or less. In light ofobtaining greater inertia, the mass is preferably 44 g or more, morepreferably 45.00 g or more. In light of satisfying the regulation ofUSGA, the mass is preferably 45.93 g or less.

When the golf ball has a diameter in a range from 40 mm to 45 mm, thecompression deformation amount of the golf ball (shrinking amount of thegolf ball along the compression direction) when applying a load from 98N as an initial load to 1275 N as a final load to the golf ball ispreferably 2.0 mm or more, more preferably 2.5 mm or more, and ispreferably 4.0 mm or less, more preferably 3.5 mm or less. If thecompression deformation amount is 2.0 mm or more, the golf ball does notbecome excessively hard and thus the shot feeling thereof is better. Onthe other hand, if the compression deformation amount is 4.0 mm or less,the resilience is greater.

EXAMPLES

Next, the present invention will be described in detail by way ofexamples. However, the present invention is not limited to the examplesdescribed below. Various changes and modifications without departingfrom the spirit of the present invention are included in the scope ofthe present invention.

[Measuring Method] (1) Slab Hardness (Shore D Hardness)

Sheets with a thickness of about 2 mm were produced by injection moldingthe cover composition or the intermediate layer composition. The sheetswere stored at 23° C. for two weeks. At least three of these sheets werestacked on one another so as not to be affected by the measuringsubstrate on which the sheets were placed, and the hardness of the stackwas measured with an automatic hardness tester Digitest II availablefrom Bareiss company, provided with a Shore D type spring hardnesstester prescribed in ASTM-D2240.

(2) Core Hardness (Shore C Hardness)

The hardness of the core was measured with an automatic hardness testerDigitest II available from Bareiss company. The Shore C hardnessmeasured at the surface of the core was adopted as the surface hardnessof the core. In addition, the core was cut into two hemispheres toobtain a cut plane, and the Shore C hardness measured at the centralpoint of the cut plane was adopted as the center hardness of the core.

(3) Compression Deformation Amount (mm)

The deformation amount of the core along the compression direction(shrinking amount of the core along the compression direction), whenapplying a load from an initial load of 98 N to a final load of 1275 Nto the core, was measured.

(4) Storage Modulus of Paint Film

The golf ball was cut into two hemispheres, and after the hemisphere wassteadily arranged, an indenter was indented from a vertical directioninto the surface of the paint film on the hemisphere, and the storagemodulus of the paint film was measured at the frequencies of 1 Hz, 10Hz, 105 Hz respectively with the following measuring method. It is notedthat the above measurement was conducted at five spots, and the averagevalue thereof was adopted as the storage modulus of that paint film.

Measuring apparatus: “TI950 Tribo Indenter” available from Hysitron,Inc.

Indenter specification: Berkovich type

Test load (maximum indenting load): 100 μN

Frequency: 1 Hz, 10 Hz, 105 Hz

Measuring environment: 23° C., RH 50%, in the atmosphere

(5) Elastic Modulus (GPa) and Hardness (GPa) of Paint Film

The golf ball was cut into two hemispheres, and after the hemisphere wassteadily arranged, an indenter was indented from a vertical directioninto the surface of the paint film on the hemisphere, and the elasticmodulus and the hardness of the paint film were calculated respectivelybased on the load-displacement curve measured with the followingmeasuring method. It is noted that the above measurements were conductedat five spots respectively, and the average value thereof was adopted asthe elastic modulus and the hardness of that paint film respectively.

Measuring apparatus: “TI950 Tribo Indenter” available from Hysitron,Inc.

Indenter specification: Berkovich type

Indenting depth (maximum indenting depth): 300 nm

Measuring environment: 23° C., RH 50%, in the atmosphere

(6) Thickness of Paint Film (μm)

The golf ball was cut into two hemispheres, and the cross section of thepaint film on the hemisphere was observed with a microscope (VHX-1000available from Keyence Corporation) to obtain the thickness of the paintfilm.

(7) 10% Elastic Modulus of Paint Film (kgf/cm²)

The 10% elastic modulus of the paint film was measured according to JISK7161 (2014). Specifically, the base material and the curing agent wereblended to prepare a paint, and the obtained paint was dried and curedat 40° C. for 4 hours to prepare a paint film (thickness: 0.05 mm). Thepaint film was punched out to prepare a test piece according to the testpiece type 2 (width of parallel part: 10 mm, gauge length: 50 mm)prescribed in JIS K7127 (1999). The tensile test of the test piece wasconducted with a precision universal tester (Autograph (registeredtrademark) available from Shimazu Corporation) under testing conditionsof a length between grips: 100 mm, a tensile speed: 50 mm/min and atesting temperature: 23° C.

(8) Spin Rate on Approach Shots (rpm)

A sand wedge (CG 15 forged wedge (58°) available from Cleveland Golf)was installed on a swing machine available from True Temper Sports, Inc.The golf ball was hit at a head speed of 10 m/s, and the spin rate (rpm)thereof was measured by continuously taking a sequence of photographs ofthe hit golf ball. The measurement was conducted ten times for each golfball, and the average value thereof was adopted as the spin rate.

(9) Shot Feeling

An actual hitting test was carried out by ten amateur golfers (highskilled persons) using a sand wedge (CG 15 forged wedge (58°) availablefrom Cleveland Golf). In accordance with the number of people whoanswered the shot feeling was good (feeling like that the golf ball waslifted on the club face, feeling like that the golf ball gripped on theclub surface, feeling like that the spin was imparted, feeling like thatthe golf ball was stuck on the club face, etc.), the golf balls wereevaluated as follows.

E (Excellent): 8 or more

G (Good): 5 to 7

F (Fair): 3 to 4

P (Poor): 2 or less

(10) Stain Resistance

The golf ball was immersed for 30 seconds in an aqueous solution oftincture of iodine obtained by diluting a tincture of iodine (an ethanolsolution containing 6 mass % of iodine and 4 mass % of potassium iodide)to 40 times, and then taken out. After the extra aqueous solution oftincture of iodine adhered on the surface of the golf ball was wipedoff, color tones (L, a, b) of the golf ball before and after theimmersion were measured with a color difference meter (CM3500D availablefrom Konica Minolta Inc.), and the color difference (ΔE) was calculatedaccording to the following equation. It is noted that a larger colordifference (ΔE) value means a larger color change extent.

ΔE=[(ΔL)²+(Δa)²+(Δb)²]^(1/2)

Evaluation Standard

E (Excellent): ΔE is 15 or less

G (Good): ΔE is more than 15 and 20 or less

P (Poor): ΔE is more than 20

1. Production of Core

The core rubber compositions having the formulations shown in Table 1were kneaded and heat pressed in upper and lower molds, each having ahemispherical cavity, under the conditions show in Table 1 to producespherical cores.

TABLE 1 Core rubber composition No. I II Formulation Polybutadienerubber 100 100 (parts by mass) Zinc acrylate 23.5 30.5 Zinc oxide 5 10Barium sulfate Appropriate Appropriate amount amount 2-Thionaphthol —0.1 Bis(pentabromophenyl) — 0.3 disulfide Dicumyl peroxide 0.95 0.7Benzoic acid — 2 Molding Temperature (° C.) 155 150 conditions Time(min) 18 19 Compression deformation amount (mm) 3.5 3.3 Center hardness(Shore C) 64 53 Surface hardness (Shore C) 80 80 Hardness difference(surface − center) 16 27 (Shore C) Polybutadiene rubber: “BR730(high-cis polybutadiene)” available from JSR Corporation Zinc acrylate:“ZN-DA90S” available from Nihon Jyoryu Kogyo Co., Ltd. Zinc oxide:“Ginrei R” available from Toho Zinc Co., Ltd. Barium sulfate: “BariumSulfate BD” available from Sakai Chemical Industry Co., Ltd.2-Thionaphthol: available from Tokyo Chemical Industry Co., Ltd.Bis(pentabromophenyl) disulfide: available from Sumitomo Seika ChemicalsCo., Ltd. Dicumyl peroxide: “Percumyl (registered trademark) D”available from NOF Corporation Benzoic acid: available fromSigma-Aldrich Co. LLC. (purity: at least 99.5 mass %)

2. Preparation of Intermediate Layer Composition and Cover Composition

According to the formulations shown in Tables 2 and 3, the materialswere mixed with a twin-screw kneading extruder to prepare theintermediate layer compositions and the cover compositions in a pelletform. The extruding conditions were a screw diameter of 45 mm, a screwrotational speed of 200 rpm, and screw L/D=35, and the mixture washeated to 200° C. to 260° C. at the die position of the extruder.

TABLE 2 Intermediate layer/cover composition No. a b c Formu- Surlyn8150 — — 32.5 lation Surlyn 9150 — — 32.5 (parts by Polyamide 6 — — 35mass) Himilan AM7337 26 — — Himilan AM7329 26 55 — Himilan 1555 — 45 —Rabalon T3221C 48 — — Barium sullate Appropriate Appropriate Appropriateamount amount amount Titanium oxide 6 3 4 Material hardness (Shore D) 3562 72 Surlyn 8150: sodium ion-neutralized ethylene-methacrylic acidcopolymer ionomer resin available from E. I. du Pont de Nemours andCompany Surlyn 9150: zinc ion-neutralized ethylene-methacrylic acidcopolymer ionomer resin available from E. I. du Pont de Nemours andCompany Polyamide 6: available from Toray Industries, Inc. HimilanAM7337: sodium ion-neutralized ethylene-methacrylic acid copolymerionomer resin available from Du Pont-Mitsui Polychemicals Co., Ltd.Himilan AM7329: zinc ion-neutralized ethylene-methacrylic acid copolymerionomer resin available from Du Pont-Mitsui Polychemicals Co., Ltd.Himilan 1555: sodium ion-neutralized ethylene-acrylic acid copolymerionomer resin available from Du Pont-Mitsui Polychemicals Co., Ltd.Rabalon T3221C: thermoplastic polystyrene elastomer available fromMitsubishi Chemical Co. Barium sulfate: “Barium Sulfate BD” availablefrom Sakai Chemical Industry Co., Ltd. Titanium oxide: A220 availablefrom Ishihara Sangyo Kaisha, Ltd.

TABLE 3 Cover composition No. A B Formulation Elastollan NY80A 100 —(parts by mass) Elastollan NY97A — 100 Titanium oxide 4 4 Ultramarineblue 0.04 0.04 Material hardness (Shore D) 27 47 Elastollan NY 80A:thermoplastic polyurethane elastomer available from BASF JapanCorporation Elastollan NY 97A: thermoplastic polyurethane elastomeravailable from BASF Japan Corporation Titanium oxide: A220 availablefrom Ishihara Sangyo Kaisha, Ltd.

3. Production of Golf Ball Body Golf Ball Bodies No. 1 to 7

The cover composition in the pellet form obtained above was directlyinjection molded onto the spherical core obtained above to produce thecover. The upper and lower molds for molding have a semispherical cavityand a retractable hold pin for holding the spherical core. When formingthe cover, the hold pin was protruded to hold the core, and the covercomposition heated to 260° C. was injected within 0.3 second into themold held under a pressure of 80 tons, and cooled for 30 seconds. Then,the golf ball was ejected from the mold.

Golf Ball Bodies No. 8 to 9

The intermediate layer composition obtained above was directly injectionmolded onto the core obtained above to produce the spherical body havingthe core covered with an intermediate layer. The upper and lower moldsfor molding have a semispherical cavity and a retractable hold pin forholding the spherical body. When forming the intermediate layer, thehold pin was protruded to hold the core, and the intermediate layercomposition heated to 260° C. was injected within 0.3 second into themold held under a pressure of 80 tons, and cooled for 30 seconds. Then,the spherical body was ejected from the mold. The cover composition inthe pellet form obtained above was charged into each of the depressedpart of the lower mold of the mold for molding half shells, and apressure was applied to mold the half shells. The compression molding ofthe half shells was conducted under the conditions of a moldingtemperature of 170° C., a molding time of 5 minutes and a moldingpressure of 2.94 MPa. The spherical body obtained above wasconcentrically covered with two of the half shells, and compressionmolding was conducted to form the cover. The compression molding of thecover was conducted under the conditions of a molding temperature of145° C., a molding time of 2 minutes and a molding pressure of 9.8 MPa.

4. Preparation of Polyol Composition

As the polyol component, polyoxytetramethylene glycol (PTMG, numberaverage molecular weight: 650) and trimethylolpropane (TMP) weredissolved in a solvent (toluene and methyl ethyl ketone). It is notedthat the molar ratio (PTMG: TMP) was 1.8:1.0. Dibutyltin dilaurate whichwas used as a catalyst was added therein in an amount of 0.1 mass % withrespect to the total amount of the base material. While keeping thetemperature of the obtained polyol solution at 80° C., isophoronediisocyanate (IPDI), as the polyisocyanate component, was added dropwiseto the polyol solution and mixed. It is noted that the molar ratio(NCO/OH) of the NCO group in the polyisocyanate component to the OHgroup in the polyol component was 0.6. After finishing the addition ofisophorone diisocyanate, stirring was continued until the isocyanategroup no longer existed. Then, the reaction liquid was cooled to a roomtemperature to prepare the urethane polyol (solid content: 30 mass %).The amount of PTMG in the obtained polyol composition was 67 mass %, thehydroxyl value of the solid component was 67.4 mgKOH/g, and the weightaverage molecular weight of the urethane polyol was 4867.

5. Preparation of Polyisocyanate Composition

30 parts by mass of the isocyanurate-modified product of hexamethylenediisocyanate (Duranate (registered trademark) TKA-100 (NCO amount: 21.7mass %) available from Asahi Kasei Chemicals Corporation), 30 parts bymass of the biuret-modified product of hexamethylene diisocyanate(Duranate 21S-75E (NCO amount: 15.5 mass %) available from Asahi KaseiChemicals Corporation), and 40 parts by mass of theisocyanurate-modified product of isophorone diisocyanate (Desmodur(registered trademark) Z 4470 (NCO amount: 11.9 mass %) available fromSumika Bayer Urethane Co., Ltd.) were mixed. As the solvent, a mixedsolvent of methyl ethyl ketone, n-butyl acetate and toluene was addedtherein to adjust the concentration of the polyisocyanate component to60 mass %.

6. Preparation of Paint Film

The surface of the golf ball body obtained above was treated withsandblast and marked. The paint having the formulations shown in Table 4were applied with a spray gun, and dried for 24 hours in an oven at 40°C. to obtain the golf balls having a mass of 45.3 g. The application ofthe paint was conducted as follows. The golf ball body was placed in arotating member provided with three prongs, and the rotating member wasallowed to rotate at 300 rpm. The application of the paint was conductedby spacing a spray distance (7 cm) between the air gun and the golf ballbody, and moving the air gun in an up and down direction. Theapplication of the paint was conducted under the spraying conditions ofspraying air pressure: 0.15 MPa, compressed air tank pressure: 0.10 MPa,painting time per one application: one second, atmosphere temperature:20° C. to 27° C., and atmosphere humidity: 65% or less. Evaluationresults regarding the obtained golf balls are shown in Table 4.

TABLE 4 Golf ball No. 1 2 3 4 5 Core Core No. I I I I I Diameter (mm)38.7 38.7 38.7 38.7 38.7 Center hardness (Shore C) 64 64 64 64 64Surface hardness (Shore C) 80 80 80 80 80 Hardness difference (Shore C)16 16 16 16 16 Intermediate layer Intermediate layer composition No. — —— — — Material hardness (Shore D) — — — — — Thickness (mm) — — — — —Cover Cover composition No. b b b b b Material hardness (Shore D) 62 6262 62 62 Thickness (mm) 2.0 2.0 2.0 2.0 2.0 Paint film Paint Mass ratio(base material/curing agent) 2.6 6.4 6.8 8.3 20.0 Molar ratio (NCO/OH)1.60 0.65 0.61 0.50 0.20 Elastic modulus (GPa) 0.660 0.510 0.160 0.0840.041 Hardness (GPa) 0.030 0.019 0.004 0.001 0.001 Storage modulus(GPa)/1 Hz 0.950 0.752 0.342 0.104 0.075 Storage modulus (GPa)/10 Hz1.050 0.953 0.447 0.219 0.156 Storage modulus (GPa)/105 Hz 1.280 1.1920.659 0.371 0.242 Slope of linear approximation curve 0.0029 0.00350.0027 0.0022 0.0013 10% elastic modulus (kgf/cm²) 286 75 65 40 3Thickness (μm) 10 10 10 10 10 Ball evaluation Spin rate on approachshots (rpm) 3650 3950 4000 4100 4200 Shot feeling P E E E E Stainresistance E G G G P Golf ball No. 6 7 8 9 Core Core No. I I II IIDiameter (mm) 38.7 38.7 39.7 39.7 Center hardness (Shore C) 64 64 53 53Surface hardness (Shore C) 80 80 80 80 Hardness difference (Shore C) 1616 27 27 Intermediate layer Intermediate layer composition No. — — b bMaterial hardness (Shore D) — — 62 62 Thickness (mm) — — 1.0 1.0 CoverCover composition No. a c A B Material hardness (Shore D) 35 72 27 47Thickness (mm) 2.0 2.0 0.5 0.5 Paint film Paint Mass ratio (basematerial/curing agent) 6.8 6.8 6.8 6.8 Molar ratio (NCO/OH) 0.61 0.610.61 0.61 Elastic modulus (GPa) 0.160 0.160 0.160 0.160 Hardness (GPa)0.004 0.004 0.004 0.004 Storage modulus (GPa)/1 Hz 0.342 0.342 0.3420.342 Storage modulus (GPa)/10 Hz 0.447 0.447 0.447 0.447 Storagemodulus (GPa)/105 Hz 0.659 0.659 0.659 0.659 Slope of linearapproximation curve 0.0027 0.0027 0.0027 0.0027 10% elastic modulus(kgf/cm²) 65 65 65 65 Thickness (μm) 10 10 10 10 Ball evaluation Spinrate on approach shots (rpm) 4150 3650 4650 4250 Shot feeling E G E GStain resistance G G G G

It is apparent from the results shown in Table 4 that the golf ballcomprising a paint film which is such that a linear approximation curveobtained by a least square method has a slope in a range from 0.0015 to0.0045 when a storage modulus (GPa) of the paint film in the state ofbeing formed on the surface of the golf ball body measured by themeasuring condition 1 is plotted as a vertical axis against a measuringfrequency (Hz) as a horizontal axis, and that an elastic modulus of thepaint film in the state of being formed on the surface of the golf ballbody measured by the measuring condition 2 ranges from 0.040 GPa to0.600 GPa, has good spin performance on approach shots and good shotfeeling as well as excellent stain resistance. In particular, in thecases that the cover has a material hardness of less than 50 in Shore Dhardness (the golf balls No. 6, 8, 9), and in the cases that anintermediate layer is disposed between the core and the cover, and thehardness difference (intermediate layer−cover) between the intermediatelayer and the cover ranges from 10 to 60 in Shore D hardness (the golfballs No. 8, 9), the spin performance on approach shots is extremelyenhanced.

This application is based on Japanese patent application No. 2016-253563filed on Dec. 27, 2016, the content of which is hereby incorporated byreference.

1. A golf ball comprising a golf ball body and a paint film formed on asurface of the golf ball body, wherein the paint film is such that alinear approximation curve obtained by a least square method has a slopein a range from 0.0015 to 0.0045 when a storage modulus (GPa) of thepaint film in a state of being formed on the surface of the golf ballbody measured by the following measuring condition 1 is plotted as avertical axis against a measuring frequency (Hz) as a horizontal axis,and that an elastic modulus of the paint film in the state of beingformed on the surface of the golf ball body measured by the followingmeasuring condition 2 ranges from 0.040 GPa to 0.600 GPa: <Measuringcondition 1> Measuring apparatus: “TI950 Tribo Indenter” available fromHysitron, Inc. Indenter specification: Berkovich type Test load (maximumindenting load): 100 μN Frequency: 1 Hz, 10 Hz, 105 Hz Measuringenvironment: 23° C., RH 50%, in the atmosphere; <Measuring condition 2>Measuring apparatus: “TI950 Tribo Indenter” available from Hysitron,Inc. Indenter specification: Berkovich type Maximum indenting depth: 300nm Measuring environment: 23° C., RH 50%, in the atmosphere.
 2. The golfball according to claim 1, wherein the linear approximation curve hasthe slope in a range from 0.0020 to 0.0040.
 3. The golf ball accordingto claim 1, wherein the storage modulus of the paint film in the stateof being formed on the surface of the golf ball body at the measuringfrequency of 1 Hz ranges from 0.100 GPa to 0.850 GPa.
 4. The golf ballaccording to claim 1, wherein the storage modulus of the paint film inthe state of being formed on the surface of the golf ball body at themeasuring frequency of 10 Hz ranges from 0.200 GPa to 1.000 GPa.
 5. Thegolf ball according to claim 1, wherein the storage modulus of the paintfilm in the state of being formed on the surface of the golf ball bodyat the measuring frequency of 105 Hz ranges from 0.300 GPa to 1.200 GPa.6. The golf ball according to claim 1, wherein a hardness of the paintfilm in the state of being formed on the surface of the golf ball bodymeasured by the above measuring condition 2 ranges from 0.001 GPa to0.020 GPa.
 7. The golf ball according to claim 1, wherein the paint filmhas a thickness in a range from 5 μm to 50 μm.
 8. The golf ballaccording to claim 1, wherein a base resin constituting the paint filmis a polyurethane obtained through a reaction between a polyolcomposition and a polyisocyanate composition.
 9. The golf ball accordingto claim 8, wherein the polyisocyanate composition contains anisocyanurate-modified product of hexamethylene diisocyanate, abiuret-modified product of hexamethylene diisocyanate and anisocyanurate-modified product of isophorone diisocyanate.
 10. The golfball according to claim 8, wherein the polyol composition contains aurethane polyol.
 11. The golf ball according to claim 8, wherein in areaction between the polyol composition and the polyisocyanatecomposition, a molar ratio (NCO/OH) of an isocyanate group (NCO group)in the polyisocyanate composition to a hydroxyl group (OH group) in thepolyol composition ranges from 0.15 to 1.20.
 12. The golf ball accordingto claim 1, wherein the golf ball body comprises a core and a covercovering the core.
 13. The golf ball according to claim 12, wherein thegolf ball body further comprises at least one intermediate layer betweenthe core and the cover.
 14. The golf ball according to claim 13, whereina hardness difference (intermediate layer-cover) between theintermediate layer and the cover ranges from 10 to 60 in Shore Dhardness.
 15. The golf ball according to claim 13, wherein a Shore Dhardness ratio (intermediate layer/cover) of the intermediate layer tothe cover ranges from 1.1 to
 5. 16. The golf ball according to claim 13,wherein the intermediate layer has a material hardness ranging from 50to 80 in Shore D hardness.
 17. The golf ball according to claim 12,wherein a hardness difference (Hs−Ho) between a surface hardness Hs ofthe core and a center hardness Ho of the core ranges from 10 to 50 inShore C hardness.
 18. The golf ball according to claim 17, wherein thesurface hardness Hs of the core ranges from 60 to 100 in Shore Chardness.
 19. The golf ball according to claim 17, wherein the centerhardness Ho of the core ranges from 40 to 80 in Shore C hardness.